Approximately 5 million spine surgeries are performed annually worldwide. Traditional, manual surgery is known as freehand surgery. Typically, for such procedures, a 3D scan (e.g., a CT and/or MRI) scan is performed prior to surgery. A CT scan is typically performed for bony tissue (e.g., vertebra), and an MRI scan is typically performed for soft tissue (e.g., discs).
Reference is made to FIG. 1A, which is a schematic illustration of a typical set up of an orthopedic operating room, for procedures that are performed in a freehand manner. Typically, in freehand procedures, although the CT and/or MRI scan is examined by the surgeon when preparing for surgery, no use is made of the CT and/or MRI images during surgery. Rather, the surgery is typically performed under 2D x-ray image guidance (also referred to as fluoroscopic guidance), the 2D x-rays typically being acquired using an x-ray C-arm. FIG. 1A shows a surgeon 10 performing a procedure using intraprocedural x-ray images that are acquired by a C-arm 34, and displayed on a display 12. Freehand surgery in which there is significant use of x-rays is known as fluoroscopy-guided surgery. X-ray C-arms are ubiquitous, familiar to surgeons, useful for acquiring real-time images, tool-neutral (i.e., there is no requirement to use orthopedic tools that are adapted specifically for imaging by the x-ray C-arm), and relatively inexpensive. A growing proportion of spinal surgeries are performed using a minimally-invasive surgery (also known as “MIS,” or in the case of spine surgery, minimally-invasive spine surgery, which is also known as “MISS”), or “mini-open” surgery. In contrast to open surgery, in which an incision is made along the applicable segment of the spine upon which surgery is performed, in minimally-invasive surgery, very small incisions are made at the insertion point of tools. In “mini-open” surgery, incisions are made that are smaller than in open surgery and larger than in minimally-invasive surgery. Typically, the less invasive the type of surgery that is performed, the greater the use of x-ray imaging for assisting the procedure. There is evidence that less invasive procedures that are performed under fluoroscopic guidance are more accurate than open procedures. However, the use of real-time fluoroscopic guidance typically exposes the patient, as well as the surgeon and the support staff to a relatively large amount of harmful radiation.
A minority of procedures are performed using Computer Aided Surgery (CAS) systems that provide navigation and/or robotics. Such systems typically make use of CT and/or MRI images that are generated before the patient is in the operating room, or when the patient is within the operating room, but typically before an intervention has commenced. The CT and/or MRI images are registered to the patient's body, and, during surgery, tools are navigated upon the images, the tools being moved manually, robotically or both.
Typically, in CAS procedures, a uniquely-identifiable location sensor is attached to each tool that needs to be tracked by the CAS system. Each tool is identified and calibrated at the beginning of the procedure. In addition, a uniquely-identifiable reference sensor is rigidly attached to the organ. In the case of spinal surgery, the reference sensor is typically drilled into the sacrum or spine, and, if surgery is performed along a number of vertebrae, the reference sensor is sometimes moved and drilled into a different portion of the spine, mid-surgery, in order to always be close to the surgical site. The images to be navigated upon (e.g., CT, MRI), which are acquired before the patient is in the operating room, or when the patient is within the operating room, but before an intervention has commenced, are registered to the patient's body or a portion thereof. In order to register the images to the patient's body, the current location of the patient's body is brought into the same reference frame of coordinates as the images using the reference sensor. The location sensors on the tools and the reference sensor on the patient's body are then tracked in order to determine the locations of the tools relative to the patient's body, and a symbolic representation of the tool is displayed upon the images that are navigated upon. Typically, the tool is tracked in 5-6 degrees of freedom.
There are various techniques that are utilized for the tracking of tools, and corresponding location sensors are used for each technique. One technique is infrared (“IR”) tracking, whereby an array of cameras track active IR lights on the tools and the patient's body, or an array of beams and cameras tracks passive IR reflectors on the tools and the patient's body. In both categories of IR tracking, lines of sight must be maintained at all times between the tracker and the tools. For example, if the line of sight is blocked by the surgeon's hands, this can interfere with the tracking. Another technique is electromagnetic or magnetic tracking, whereby a field generator tracks receivers, typically coils, on the tools and the patient's body. For those latter techniques, environmental interferences from other equipment much be avoided. In each of the techniques, the location sensors of the navigation system are tracked using tracking components that would not be present in the operating room in the absence of the navigation system (i.e., the location sensors do not simply rely upon imaging by imaging devices that are typically used in an orthopedic operating room in the absence of the navigation system).
A further technique that can be used with a robotically-driven tool is to start with the tool at a known starting point relative to the patient's body, and to then record motion of the tool from the starting point. Alternatively, such tools can be tracked using the above-described techniques.
Given the nature of CAS procedures, the equipment required for such procedures is typically more expensive than that of non-CAS procedures (non-CAS procedures including open procedures, mini-open procedures, or minimally-invasive procedures that are not computer aided with respect to the guidance of tools). Such procedures typically limit tool selection to those fitted with location sensors as described above, and typically require such tools to be individually identified and calibrated at the beginning of each surgery.